JP3700207B2 - Automatic exposure control device, automatic exposure control method, and imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automatic exposure control device and an automatic exposure control method in an imaging apparatus, and more specifically, can perform backlight and over-order light determination in consideration of the state of a subject, and can also perform automatic subject tracking systems and hands-free. The present invention relates to an automatic exposure control device and an automatic exposure control method that are effective for photographing and the like.
[0002]
[Prior art]
In certain types of video cameras and still cameras, an object in the screen is specified from the line of sight looking through the viewfinder, and the luminance values in the area near the object are integrated, and automatic exposure control is performed so as to obtain a constant value.
[0003]
Further, other general video cameras and still cameras do not specify a subject, determine back light and over-order light only from a luminance histogram in the screen, and automatically control exposure.
[0004]
[Problems to be solved by the invention]
In a conventional general video camera, a subject cannot be specified and extracted. Therefore, for example, when attempting to shoot a subject in a backlight state, it is not possible to determine whether the subject is shining white in the screen or whether the subject is crushed black. As a result, in the case of a dark subject in a large-area light background, there is a problem in that the subject is crushed in black even if a slight backlight correction is applied due to the shape of the luminance histogram.
[0005]
The same applies to over-order lighting conditions, because it is not possible to determine which subject is over-satisfied, and the over-order light judgment cannot be satisfied. There is a problem that exposure is opened by a dark area occupying a large area, and the subject flies white.
[0006]
The present invention has been made in view of such a problem, and an automatic exposure control device, an automatic exposure, which can determine an appropriate backlight and overorder light by specifying a subject and performing extraction. It is an object to provide a control method and an imaging apparatus.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, an automatic exposure control apparatus according to the present invention includes an image storage unit that periodically stores an image signal from an image sensor, and a setting frame based on image information stored in the image storage unit. The subject model creating means for creating a subject model in the luminance / color difference space based on the obtained image information in the setting frame, and stored in the image storage means using the subject model Subject extraction means for extracting a subject from image information, brightness histogram creation means for creating a histogram relating to screen brightness from image information stored in the image storage means, and calculation of an average brightness value of the subject from the image information of the subject Subject brightness calculation means, and determination means for determining whether the subject is in a backlight state or an over-order light state from the histogram and the average brightness value , And a exposure control means for controlling exposure on the basis of an output of said determining means, said determining means, subject by the subject extraction unit is determined to be present in the screen, the object calculated by the object luminance calculation means The luminance is smaller than a predetermined threshold, and the frequency near the peak value below the first luminance of the luminance histogram of the screen created by the luminance histogram creating means and the second luminance greater than the first luminance is greater than or equal to the second luminance. When the sum of the frequencies in the vicinity of the peak value exceeds a predetermined threshold value, it is determined that the backlight is in the backlight state, and it is determined that the subject does not exist in the screen by the subject extraction unit, and is created by the luminance histogram creation unit The frequency near the peak value below the first luminance in the luminance histogram of the screen and the frequency near the peak value above the second luminance greater than the first luminance. Sum exceeds a predetermined threshold value, if the luminance of the pixels below a predetermined threshold value to the center of the screen is equal to or greater than the predetermined number threshold value, and wherein the determining the backlit state.
[0008]
The automatic exposure control method according to the present invention is a method in which an image signal from an image sensor is periodically stored in an image storage means, and automatic exposure control is performed using image information stored in the image storage means. A subject model creating step for obtaining image information in a setting frame from image information stored in the image storage means to create a subject model in a luminance / color difference space, and using the subject model, the image storage means A subject extraction step for extracting a subject from the image information stored in the image, a luminance histogram creation step for creating a histogram relating to the brightness of the screen from the image information stored in the image storage means, and an average of the subjects from the image information of the subject The subject luminance calculation step for calculating the luminance value, the histogram and the average luminance value are in a backlight state or are in excessive order. A determination step for determining whether the subject is in a state and an exposure control step for controlling exposure based on the output of the determination means. In the determination step, the subject extraction step determines that the subject is present in the screen. The frequency of the subject brightness calculated by the subject brightness calculation is smaller than a predetermined threshold value, and the frequency near the peak value below the first brightness of the brightness histogram of the screen created by the brightness histogram creating means and the first brightness When the sum of the frequencies near the peak value above the second luminance greater than the luminance exceeds a predetermined threshold value, it is determined that the backlight is in the backlit state, and the subject extracting means determines that the subject does not exist in the screen. The frequency near the peak value below the first brightness of the brightness histogram of the screen created in the brightness histogram creating step and the first brightness The sum of the frequency of the peak value near the second luminance or exceeds a predetermined threshold Kii, when the luminance of the pixels below a predetermined threshold value to the center of the screen is equal to or greater than the predetermined number threshold value, it is determined that the backlit It is characterized by.
[0009]
An imaging apparatus according to the present invention includes the automatic exposure control apparatus according to the present invention and an imaging element that outputs an image signal to the automatic exposure control apparatus.
[0010]
According to the present invention, the subject can be specified. Therefore, when shooting a dark subject in a large area of light background, the backlight correction is performed by opening the exposure rather than the exposure by the normal full screen integration. It is possible to clearly capture a dark subject, and conversely, in the case of a bright subject with a large area, the exposure can be narrowed down and the bright subject can be captured with an appropriate exposure.
[0011]
Similarly, when shooting a bright subject in a large area of dark background, the over-order light correction is performed to narrow down the exposure rather than the exposure based on the normal integral of the entire screen. On the contrary, in the case of a dark subject with a large area, the exposure is opened, and the dark subject can be caught with an appropriate exposure.
[0012]
In order to extract the subject from the screen, a subject model in the luminance / color difference space that has been confirmed to be effective as a subject tracking system is used. This is a model that represents the subject from the subject information in the setting frame. This is developed in a three-dimensional space of color differences, and for each pixel in the screen, a pixel that applies to the model is extracted as a pixel constituting the subject.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail below in the order of [1] an imaging apparatus to which the present invention is applied [2] processing in a tracking signal processing circuit [3] specific configuration example of tracking signal processing, with reference to the drawings. .
[0014]
[1] Imaging Device to which the Present Invention is Applied FIG. 1 is a block diagram showing a configuration of an imaging device to which the present invention is applied. In the following description, the luminance of the component video is Y, R−Y is R, and BY is B, and the image in the image memory 11 described later is the i-th pixel in the vertical direction and the j-th pixel in the horizontal direction. The values are Yij for Y, Rij for R, and Bij for B.
[0015]
As shown in FIG. 1, an image pickup apparatus to which the present invention is applied includes a lens block 1 having a lens 2, an iris 3, and an image pickup device 4 made of, for example, a CCD, and an image pickup created by the lens block 1. A signal separation / automatic gain adjustment circuit 5 that performs sample-and-hold and automatic gain adjustment on the signal S1, an analog / digital conversion circuit 6 that digitizes the output signal S2 of the signal separation / automatic gain adjustment circuit 5, and an analog / A digital camera processing circuit 7 for performing predetermined camera signal processing on the output of the digital conversion circuit 6 and a digital / analog conversion circuit 8 for converting the Y signal and C signal formed by the digital camera processing circuit 7 into analog signals are provided. ing.
[0016]
The imaging apparatus to which the present invention is applied includes an iris control circuit 9 that generates an iris control signal S9 for controlling the iris motor 12 based on the Y, R, and B signals formed by the digital camera processing circuit 7, and An iris motor 12 that is rotationally controlled by an iris control signal S9 and adjusts the degree of aperture of the iris 3 is provided. Here, the iris control circuit 9 is composed of, for example, an image memory 10 composed of a frame memory and a tracking signal processing circuit 11 composed of a microprocessor.
[0017]
Next, the operation of the imaging device shown in FIG. 1 will be described. In this imaging device, imaging light arriving from a subject passes through the lens 2 and iris 3 of the lens block unit 1 and is received by the imaging device 4, and an imaging output signal S 1 representing the subject image is sent to the signal separation / automatic gain adjustment circuit 5. give.
[0018]
The signal separation / automatic gain adjustment circuit 5 samples and holds the imaging output signal S1, and gain is controlled so that the imaging output signal S2 has a predetermined gain by a control signal from an auto iris (AE) system (not shown). . The imaging output signal S2 is supplied to the digital camera processing circuit 7 via the analog / digital conversion circuit 6.
[0019]
The digital camera processing circuit 7 forms Y, C and R and B based on the imaging output signal S2, and sends Y and C as a video signal S3 via the digital / analog conversion circuit 8.
[0020]
Further, the digital camera processing circuit 7 supplies Y, R, and B to the iris control circuit 9 as the subject tracking detection image signal S4, and the iris control circuit 9 uses the iris tracking detection signal image S4 to create the iris control signal S9. Controls the iris motor 12 to generate a control signal S10 for the iris 3 provided in the lens block unit 1.
[0021]
The iris control circuit 9 writes R, B, and Y into the image memory 10 as the subject tracking detection image signal S4. This writing is performed in units of pixels independently of Y, R, and B after receiving the write permission signal S5 sent from the tracking signal processing circuit 11.
[0022]
For example, when the storage of the subject tracking detection image signal S4 for one frame is completed in the image memory 10, the image memory 10 sends a read permission signal S6 to the tracking signal processing circuit 11. After confirming the read permission signal S6, the tracking signal processing circuit 11 reads the Y, R, and B data S8 at a predetermined position in the image memory 10 by giving a predetermined memory address S7 to the image memory 10. Capture inside. The tracking signal processing circuit 11 performs subject position calculation processing using the captured data S8 (details will be described later). After the processing is completed, the write permission signal S5 is given to the image memory 10 again. After confirming the write permission signal S5, the image memory 10 writes the subject tracking detection image signal S4 for the next one frame.
[0023]
The tracking signal processing circuit 11 extracts a subject, calculates the subject brightness, and creates a brightness histogram of the screen, calculates an appropriate exposure control value from the information, and supplies the iris control signal S9 to the iris motor 12. .
[0024]
The rotation direction and amount of rotation of the iris motor 12 are controlled by the iris control signal S9, and the iris degree of the iris 3 is adjusted.
[0025]
[2] Processing in Tracking Signal Processing Circuit Next, an outline of processing performed in the tracking signal processing circuit 11 will be described with reference to FIG.
[0026]
First, frame-weighted photometry processing P0 is executed to identify the subject. In this process, the exposure is automatically controlled so that the luminance in the frame displayed on the screen becomes the set value α. By this processing P0, the subject can be set to a state having appropriate luminance.
[0027]
Next, subject information acquisition processing P1 is executed. In this process, first, subject information of a region D0 (for example, a block of 5 × 5 pixels) in the center of the screen is acquired on the condition that the subject is in the center of the screen.
[0028]
Next, the model determination process P2 is executed. In this process, a subject model including a permissible error in a quadratic approximate curve for Y and R and Y and B is determined based on the subject information obtained in the process P1.
[0029]
Next, each pixel determination process P3 is executed. In this process, the subject model obtained in the process P2 is used to determine whether or not each pixel on the screen is a candidate point of the subject.
[0030]
Next, a process P4 for determining whether or not the subject exists within the frame is executed. This process determines whether or not the subject is within the frame by determining whether or not the number of pixels determined to be a candidate point of the subject in process P3 exceeds a certain threshold β. When it is below, it is determined that the subject does not exist in the screen, and when it exceeds β, it is determined that it exists.
[0031]
Next, subject brightness calculation processing P5 is executed. In this process, an average brightness value is obtained for the subject candidate pixels extracted in process P3, and the subject brightness is calculated.
Next, luminance histogram creation processing P6 is executed. This process creates a histogram for the luminance of the pixels on the entire screen.
[0032]
Next, the backlight determination process P7 is executed. In this process, it is determined whether the subject is backlit or not backlit based on the subject brightness calculated in process P5 and the brightness histogram created in process P6.
[0033]
If it is determined in the process P7 that the light is backlit, the subject model change process P7a is executed. This process changes the subject model created in process P2. On the other hand, if it is determined to be backlit until just before and it is determined not to be backlit in this process P7, process P7b is executed. In this process P7b, the subject model changed in process P7a is returned to the model at the time of subject setting.
[0034]
After returning the subject model to the model at the time of subject setting in the process P7b, the over-order light determination process P8 is executed. In this process, it is determined whether or not over-order light is detected or not based on the subject brightness calculated in process P5 and the brightness histogram created in process P6.
[0035]
Next, an exposure control amount determination process P9 is executed. In this process, the final exposure control amount is determined according to the state determined in the processes so far.
[0036]
[3] Specific Configuration Example of Tracking Signal Processing An example of a specific configuration relating to the characteristic of each processing in FIG. 2 will be described below.
[0037]
Process P0 is performed after the photographer operates the remote commander or the like to move the frame within the screen to match the subject. FIG. 3 shows a functional block diagram of the automatic exposure control system. In this figure, the iris is the iris 3 in FIG. 1, the optical processing system is from the image sensor 4 to the A / D conversion circuit 6 in FIG. 1, the signal processing unit is in the digital camera processing circuit 7 and the image memory 10, and the screen brightness is increased. The integration unit, the specific area luminance integration unit, the multiplier, and the comparator correspond to the tracking signal processing circuit 11 and the iris motor 12, respectively.
[0038]
In FIG. 3, conventionally known normal exposure control, as shown by the flow of thin lines, controls the iris by comparing the weighted integral value Yitg of the screen brightness with a preset reference value Yref. Here, Yitg is an integral value of luminance obtained by dividing the screen into three as shown in FIG. 4 and giving weights to the respective regions, and can be expressed by the following equation [1].
[0039]
Yitg = (W1 × Y1 + W2 × Y2 + W3 × Y3) / N (1)
However, in this formula [1], W1 is the weight in region 1, W2 is the weight in region 2, W3 is the weight in region 3, Y1 is the integrated luminance value in region 1, and Y2 is the luminance in region 2. The integral value, Y3 is the luminance integral value in region 3, and N is the number of pixels in the entire screen.
[0040]
On the other hand, when performing frame-weighted metering in the present embodiment, as indicated by the flow of the thick line, the reference value Yref is multiplied by the gain G = Yref / Yfrm, and the reference value is raised or lowered. Here, Yfrm is the average luminance value within the frame. That is, in this case, the exposure affects the luminance of the entire screen, but the luminance in the frame is weighted.
[0041]
In the process P1, since the set of (Yij, Rij, Bij) in the region D0 has noise and is only a representative point of the subject, in order to give the subject information a certain width (Yij, HRij, HBij), (Yij, LRij, LBij) are subject information.
[0042]
here,
HRij = Rij × 1.1
HBij = Bij × 1.1
LRij = Rij × 0.9
LBij = Bij × 0.9
It is. That is, the allowable error is 10%.
[0043]
In the process P2, a subject model is determined by a quadratic approximation function of R and B related to Y from the set of (Yij, HRij, HBij) and (Yij, LRij, LBij) obtained in the process P1. At this time, intercepts Rlow, Rhigh, Blow, and Bhigh on the Y axis are held as constants so that a subject model that is quadratic approximated for an arbitrary subject has a certain shape, and the following is obtained by the least square method. A0 to A4 are determined, and R and B subject models HFr (Y), HFb (Y), LFr (Y), and LFb (Y) for Y shown in the following equations [2] to [4] To decide.
[0044]
HFr (Y) = A0 × (Y−Rlow) × (Y−Rhigh) [2]
HFb (Y) = A1 × (Y−Blow) × (Y−Bhigh) [3]
LFr (Y) = A2 * (Y-Rlow) * (Y-Rhigh) ... [4]
LFb (Y) = A3 × (Y−Blow) × (Y−Bhigh) [5]
The subject model determined in this way is shown in FIG.
[0045]
The process P3 determines whether each pixel is applicable to the subject model obtained in the process P2, that is, whether both R and B fall between the two curves in FIGS. 5 (a) and 5 (b). That means
[0046]
LFr (Yij) <Rij <HFr (Yij)
And LFb (Yij) <Bij <HFb (Yij)
Then, the pixel is determined to be a part of the subject. Then, the coordinates (X, Y) of the subject are determined by obtaining the horizontal and vertical centers of gravity of the plurality of pixels determined to be part of the subject.
[0047]
In process P6, the brightness of each pixel of the entire H screen is quantized into 16 levels to create a brightness histogram.
[0048]
Conditions (1) and (2) below are conditions for determining backlighting in process P7.
(1) In process P4, it is determined that the subject is present in the screen, and the subject brightness calculated in process P5 is below a certain threshold T1, and on the low brightness side when the brightness histogram created in process P6 is less than the set value K1. The sum P1 of the vicinity of the peak value and the vicinity of the peak value on the high luminance side that is equal to or greater than the set value K2 is greater than or equal to a threshold T2.
[0049]
Here, the calculation method of P1 is demonstrated using the example shown in FIG.
Assuming that the luminance frequency in the nth gradation is E (n), the luminance peak below K1 is n = 1, and taking ± 1 as the vicinity of the peak value, the frequency sum PL1 near the low luminance side peak value. Is PL1 = E (0) + E (1) + E (2)
It becomes.
[0050]
Similarly, the luminance peak at K2 or higher is n = 11, and if it is taken as ± 1 as the vicinity of the peak value, the frequency sum PH1 in the vicinity of the high luminance side peak value is PH1 = E (10) + E (11) + E (12)
It becomes.
[0051]
Since P1 is the sum of PL1 and PH1, P1 = PL1 + PH1 = E (0) + E (1) + E (2) + E (10) + E (11) + E (12) (6)
It is.
[0052]
(2) In process P4, it is determined that the subject does not exist in the screen, P1 is equal to or greater than the threshold T2, and the number of pixels having a luminance equal to or less than a certain threshold T3 is equal to or greater than the threshold T4 in the frame set in the center of the screen. If.
[0053]
(3) In the process P7, the condition process for exiting the backlight state is as follows. That is, only when the previous state is backlight, and when P1 is equal to or less than a certain threshold T5, it is determined that the normal state is returned from the backlight state.
[0054]
As described above, when it is determined that the light is backlit in the process P7, the subject model is changed in the process P7a. FIG. 8 shows this state. As shown in this figure, the width of the subject model determined in the process P2 is increased by γ in the ± direction at the time of backlighting, and the high brightness side of the model is crushed because the subject is not brightened in the backlighting state. In the example of FIG. 8, the higher luminance side than 180 is crushed.
[0055]
Next, conditions (4) and (5) below are used to determine the excessive forward light in process P8.
(4) It is determined in the process P4 that the subject is present in the screen, and the luminance frequency sum PL2 of the subject brightness calculated in the process P5 is greater than or equal to a certain threshold T6 and less than the set value K3 of the brightness histogram set in the process P6. When the frequency sum PH2 in the vicinity of the high-luminance peak value at the set value K4 or higher is a threshold T7 or higher.
[0056]
In the example of FIG.
PL2 = E (0) + E (1)
PH2 = E (12) + E (13) + E (14)
And
[0057]
P2 = PL2 + PH2 = E (0) + E (1) + E (12) + E (13) + E (14) ... [7]
It is.
[0058]
(5) When it is determined in process P4 that the subject does not exist in the screen, P2 is equal to or higher than the threshold T7, and a pixel having a luminance equal to or lower than a certain threshold T8 is equal to or higher than the threshold T9 in the frame set in the center of the screen .
[0059]
In the process P8, a condition process for exiting the over-order light state is also performed. Conditions (6) and (7) below show the conditions for exiting from overorder light.
(6) A case where the sum P3 of gradation frequencies indicating intermediate luminances with luminances not less than the set value K5 and not more than K6 is greater than or equal to the threshold T11.
[0060]
In the example of FIG. 7, P3 = E (3) + E (4) + E (5) + E (6) + E (7)
It is.
[0061]
(7) A case where the sum P4 of the grayscale frequencies indicating high luminance with the luminance equal to or higher than the set value K7 is equal to or greater than the threshold T12.
In the example of FIG. 7, P4 = E (11) + E (12) + E (13) + E (14) + E (15)
It is.
[0062]
FIG. 9 shows a series of state transitions in the processes P7 and P8 described above, and FIG. 10 shows the transition conditions.
[0063]
In the process P9, the gain G (= Yref / Yfrm) to be multiplied by the reference value Yref in FIG. 3 is determined according to the states determined in the processes P7 and P8.
[0064]
First, when it is determined in processing P7 and processing P8 that the normal state is neither backlight nor over-order light, G = 1, and the automatic exposure control system is performed by normal weighted total integration.
[0065]
If it is determined in the process P7 that the backlight is in the backlit state or the process P8 is in the over-ordered light state, the following (8) and (9) are obtained depending on the presence of the subject.
(8) When a subject exists The subject average luminance calculated in process P5 is substituted into Yfrm, and G = Yref / Yfrm is multiplied by the reference value Yref. That is, subject photometric exposure control is performed.
[0066]
(9) When no subject exists The average luminance within the frame set at the center of the screen is substituted for Yfrm, and G = Yref / Yfrm is multiplied by the reference value Yref. That is, exposure control of the center-centered metering type is performed.
[0067]
After the exposure control amount is determined as described above, the process returns to process P3 and a series of processes are repeated.
[0068]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to accurately determine the backlight and the over-order light by specifying the subject. Appropriate exposure can be performed. For this reason, a big effect can be exhibited in the performance improvement of the conventional automatic exposure control function.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus to which the present invention is applied.
FIG. 2 is a flowchart showing processing performed in a tracking signal processing circuit.
FIG. 3 is a diagram showing functional blocks of an automatic exposure control system.
FIG. 4 is a diagram showing screen division in automatic exposure control.
FIG. 5 is a diagram illustrating a setting example of a subject model.
FIG. 6 is a diagram showing an example of a backlight state histogram;
FIG. 7 is a diagram showing an example of a histogram in an over-order light state.
FIG. 8 is a diagram illustrating an example of changing a subject model at the time of backlight determination.
FIG. 9 is a diagram showing state transition.
FIG. 10 is a diagram illustrating a condition for state transition.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 3 ... Iris, 4 ... Image sensor, 9 ... Iris control circuit, 10 ... Image memory, 11 ... Tracking signal processing circuit, 12 ... Iris motor

Claims (9)

Image storage means for periodically storing image signals from the image sensor;
Subject model creation means for obtaining image information in a setting frame from the image information stored in the image storage means, and creating a subject model in a luminance / color difference space based on the acquired image information in the setting frame;
Subject extraction means for extracting a subject from image information stored in the image storage means using the subject model;
A brightness histogram creating means for creating a histogram relating to the brightness of the screen from the image information stored in the image storage means;
Subject luminance calculating means for calculating an average luminance value of the subject from the image information of the subject;
A determination means for determining whether the backlight is in the backlight state or the over-order light state from the histogram and the average luminance value;
Exposure control means for controlling exposure based on the output of the determination means ,
The determination means determines that the subject is present in the screen by the subject extraction means, the subject brightness calculated by the subject brightness calculation means is smaller than a predetermined threshold, and the screen of the screen created by the brightness histogram creation means When the sum of the frequency near the peak value below the first luminance in the luminance histogram and the frequency near the peak value above the second luminance greater than the first luminance exceeds a predetermined threshold value, And the subject extraction means determines that the subject does not exist in the screen, and the frequency near the peak value below the first brightness of the brightness histogram of the screen created by the brightness histogram creation means and the first The sum of the frequencies near the peak value above the second luminance greater than the luminance of 1 exceeds a predetermined threshold, and a pixel having a luminance equal to or lower than the predetermined threshold is present in the center of the screen. If it is a constant equal to or higher than the threshold number, the automatic exposure control device, wherein the determining the backlit state.   The setting frame is configured to be arranged at an arbitrary position on the screen. When acquiring image information of the subject in the setting frame, the luminance in the setting frame is set to a predetermined value. The automatic exposure control apparatus according to claim 1, wherein the automatic exposure control apparatus controls the automatic exposure control apparatus.   The exposure control means includes a brightness integral value calculation means for calculating an integral value of brightness within the screen, a comparison means for comparing a preset brightness reference value with the brightness integral value, and the determination means in a backlight state. Or a means for raising and lowering the luminance reference value so that the luminance of the subject becomes a constant value when it is determined as an over-order light state, and a means for controlling exposure according to the output of the comparison means. The automatic exposure control device according to claim 1. In the state determined as the backlight state by the determining means, the frequency near the peak value below the first brightness of the brightness histogram created by the brightness histogram creating means and the second greater than the first brightness. 2. The automatic exposure control device according to claim 1, wherein when the sum of the frequencies near the peak value above the luminance is equal to or less than a predetermined threshold value, it is determined that the backlight is no longer in the backlight state, and the normal exposure control is switched . The determination means determines that the subject is present in the screen by the subject extraction means, the subject brightness calculated by the subject brightness calculation means is greater than a predetermined threshold, and the screen of the screen created by the brightness histogram creation means When the sum of the frequency sum of the luminances below the predetermined value in the luminance histogram and the frequency sum of the luminances near the peak value on the high luminance side above the predetermined luminance exceeds a predetermined threshold value, it is determined as an over-order light condition. In addition, it is determined that the subject does not exist in the screen by the subject extracting unit, and the frequency sum of luminances below a predetermined set value of the luminance histogram of the screen created by the luminance histogram creating unit, and above the predetermined luminance The sum of the frequency of luminance near the peak value on the high-intensity side exceeds a predetermined threshold value, and pixels with a luminance equal to or lower than the predetermined threshold value are equal to or greater than the predetermined threshold number in the center of the screen. That case, the automatic exposure control apparatus according to claim 1, wherein the determining an excessive follow light state. In a state in which the said determining means is determined over frontlit condition, if the number of pixels the intermediate luminance of the luminance histogram created by the luminance histogram creating means is greater than a predetermined threshold, determines that no longer excessive follow light state The automatic exposure control device according to claim 1, wherein the automatic exposure control device is switched to normal exposure control. If the number of high-luminance pixels in the luminance histogram created by the luminance histogram creation means is greater than or equal to a predetermined threshold in the state determined by the determination means as an over-order light state, it is determined that the over-order light state has been lost. The automatic exposure control device according to claim 1, wherein the automatic exposure control device is switched to normal exposure control. An image signal from an image sensor is periodically stored in an image storage means, and automatic exposure control is performed using image information stored in the image storage means,
A subject model creation step of obtaining image information in a setting frame from the image information stored in the image storage means, and creating a subject model in a luminance / color difference space based on the acquired image information in the setting frame;
A subject extraction step of extracting a subject from the image information stored in the image storage means using the subject model;
A luminance histogram creating step for creating a histogram relating to the luminance of the screen from the image information stored in the image storage means;
A subject luminance calculation step for calculating an average luminance value of the subject from the image information of the subject;
A determination step for determining whether the backlight is in a backlight state or an over-order light state from the histogram and the average luminance value;
An exposure control step for controlling exposure based on the output of the determination means,
In the determining step, it is determined that the subject is present in the screen in the subject extracting step, the subject brightness calculated by the subject brightness calculation is smaller than a predetermined threshold, and the brightness of the screen created by the brightness histogram creating means When the sum of the frequency near the peak value below the first luminance of the histogram and the frequency near the peak value above the second luminance greater than the first luminance exceeds a predetermined threshold, it is determined that the backlight is in the backlight state. Further, it is determined that the subject does not exist in the screen by the subject extraction means, and the frequency near the peak value below the first brightness of the brightness histogram of the screen created in the brightness histogram creating step and the first A pixel whose luminance is less than or equal to a predetermined threshold in the center of the screen, the sum of the frequencies near the peak value at or above the second luminance greater than If the predetermined or threshold number, the automatic exposure control method characterized by determining the backlit state. An image sensor;
Image storage means for periodically storing image signals from the image sensor;
Subject model creation means for obtaining image information in a setting frame from the image information stored in the image storage means, and creating a subject model in a luminance / color difference space based on the acquired image information in the setting frame;
Subject extraction means for extracting a subject from image information stored in the image storage means using the subject model;
A brightness histogram creating means for creating a histogram relating to the brightness of the screen from the image information stored in the image storage means;
Subject luminance calculating means for calculating an average luminance value of the subject from the image information of the subject;
A determination means for determining whether the backlight is in the backlight state or the over-order light state from the histogram and the average luminance value;
Exposure control means for controlling exposure based on the output of the determination means,
The determination means determines that the subject is present in the screen by the subject extraction means, The subject brightness calculated by the subject brightness calculating means is smaller than a predetermined threshold value, and the frequency near the peak value below the first brightness of the brightness histogram of the screen created by the brightness histogram creating means and the first When the sum of the frequencies near the peak value above the second luminance greater than the luminance exceeds a predetermined threshold value, it is determined that the backlight is in the backlit state, and the subject extracting means determines that the subject does not exist in the screen. The sum of the frequency near the peak value below the first luminance and the frequency near the peak value above the second luminance larger than the first luminance in the luminance histogram of the screen created by the luminance histogram creating means. An image pickup apparatus characterized in that when a pixel exceeds a predetermined threshold value and a pixel having a luminance equal to or lower than the predetermined threshold value is greater than or equal to a predetermined threshold number in the center of the screen, the backlight device is determined to be in a backlight state.

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